This invention is directed toward a charging system for electrochemical batteries. More particularly, the invention solves certain problems associated with charging a multiple module series arrangement of individual constituent batteries or cells making up an aggregate battery pack.
Motor vehicles driven by electric motors typically require voltages of significantly greater magnitude than those commonly utilized in conventional internal combustion engine driven motor vehicles for powering accessories. A battery pack made up of at least one series arrangement--and potentially multiple parallel connected series arrangements--of individual modules is one common way for achieving a high voltage in a manageable form. Physical characteristics from module to another are never identical even when modules are produced under the tightest control. This becomes an extremely important consideration in a series arrangement of modules wherein the discharge and charge current is identical through each module. During discharge or re-charge cycling of a series battery pack, one or another of the individual modules reaches--prior to the remaining modules reaching--certain physical discharge or re-charge limitations after which damage may occur.
For example, in conventional lead acid aqueous electrolyte batteries, discharge beyond a certain point may lead to reversal of the electrodes and permanent damage to the module. Re-charge beyond a certain point may lead to gassing of the electrolyte thereby reducing the useful life of the module. Additionally, the module reaching a fully charged state prior to the others will thereby limit the charge of the remaining modules where charging is terminated in response thereto. This "weak link" in the series chain of modules will thereby promote the situation wherein the only fully charged module is the one to first reach that state, resulting in a battery pack which never reaches its full energy capacity.